Scanning electron microscopy of some cyst nematodes

Abstract

Three Heterodera species, H. elachista, H. avenae, and H. glycines, and one Globodera species, G. rostochiensis (2nd stage larvae) were examined with a scanning electron microscope (SEM) to see if any additional information for the separation of species could be obtained. The oral discs of 2nd stage larvae presented dumbbellshape in H. elachista, elongated oval in H. avenae, a modification of dumbbell-shape in H. glycines, and oval with submedian lips in G. rostochiensis. The oral discs of males presented dumbbell-shape in H. elachista, elongated oval in H. avenae, and oval with lips in H. glycines. In mature females and cysts, H. elachista and H. glycines had the highly domed cone top with wide vulva, but with different numbers of perineal ridges, and H. avenae was distinguished from the former two species by the low domed cone top with narrow vulva. Thus, these species could be easily separated with SEM. The face views of these females were slightly dissimilar having varied rectangular oral discs with more or less concave side, but they could not be clearly separated. The two minute pores opening near the tip of each spicule located outside in H. elachista and H. glycines, but inside the spicule in H. avenae. Only in male of H. glycines the six inner labial papillary openings were observed about the oral aperture. Therefore, the morphological characters which are important in the identification and taxonomy of Heterodera species newly included the location of two minute pores on each spicule tip, the absence or presence of papillary opening, and the lip pattern of male. In view of these observations, it was recognized that the introduction of SEM technology made possible the rapid and accurate identification of cyst nematodes.